1. Field of the Invention
This invention relates to an apparatus for recording and reproducing information signals on and from a recording medium.
2. Description of the Related Art
In the field of magnetic recording, it has been a recent trend to pursue high density recording. Video tape recorders (hereinafter referred to as VTR's) also have come to increase the density of magnetic recording by lowering the travelling speed of the tape. As a result, however, it has become impossible to obtain reproduced sounds in high quality in accordance with the conventional method of recording audio signals by means of a fixed head because a required degree of relative speed is not obtainable between the head and the tape. In a conceivable method for solving this problem, the recording tracks to be formed by means of rotary heads are arranged to be longer to have audio signals recorded one after another in the extended areas of the tracks by time-base compressing the audio signals.
FIG. 1 of the accompanying drawings shows the tape transport system of the VTR of the above-stated prior art. FIG. 2 shows the recording locus formed on the magnetic tape by the same VTR. These illustrations include the magnetic tape 1; a rotary cylinder 2; heads 3 and 4 which are mounted on the rotary cylinder 2 with a phase difference of 180 degrees between them and have different azimuth angles from each other; a video recording area 5 within each of recording tracks formed on the tape 1; and an audio recording area 6 provided in each of the tracks. The video recording area 5 is formed with the tape traced by the heads 3 and 4 when the cylinder 2 rotates 180 degrees. The audio area 6 is formed by the heads 3 and 4 when the cylinder 2 rotates to a degree of angle .theta..
An audio signal which is pulse-code modulated (PCM) and time-base compressed is recorded in the audio recording area. With the audio signal thus recorded, the signal can be reproduced at a high degree of sound quality which favorably compares with signals reproduced by an audio dedicated apparatus.
Meanwhile, there has been proposed a modification of the prior art VTR of the above-stated kind, wherein: Other audio signals are arranged to be recordable also in the video recording area 5. For example, assuming that the above-stated angle .theta. is 36 degrees, five audio recording areas which are similar to the above-stated audio recording area 5 can be obtained while the rotary cylinder rotates 180 degrees. Then, with the time-base compressed audio signals arranged to be recorded in each of these areas, an audio dedicated tape recorder which is capable of recording audio signals in a total of six channels can be obtained by this arrangement. FIG. 3 shows the tape transport system of that tape recorder. FIG. 4 shows the recording locus of the tape recorder formed on the tape. In FIGS. 3 and 4, the same reference numerals as those shown in FIGS. 1 and 2 indicate the same parts.
Referring to FIGS. 3 and 4, while the head 3 or 4 is tracing the tape 1 between points A and B; B and C; C and D; D and E; E and F; and F and G, audio signals are recorded in areas CH1 to CH6. Each of these audio signals is recordable in each of these areas independently of others. While the so-called azimuth overlapped writing is arranged to be accomplished, the recording tracks within each of these areas CH1 to CH6 do not have to be formed in perfect alignment. While pilot signals for tracking control are also recorded in each of these areas, they have no correlation with those of other areas.
The above-stated multi-channel audio tape recorder may be arranged to record and reproduce only in the forward direction of the tape (for example, in the direction of arrow 7 of FIG. 3) for all the channels. However, the operability of the tape recorder may be improved by arranging it to be recordable and reproducible not only in the forward direction but also in the reverse direction. In the case of such arrangement, the recording or reproduction is, for example, performed while the tape is travelling in the direction of arrow 7 for the areas CH1 to CH3 and in the direction of arrow 9 for the areas CH4 to CH6. Therefore, the inclination of the recording tracks formed in the areas CH1 to CH3 somewhat differs from that of the tracks formed in the areas CH4 to CH6. As regards to a difference in relative speed, however, a difference due to the travel of the tape in the opposite directions is much smaller than a difference due to the revolution of the heads 3 and 4 and thus presents no problem.
FIG. 5 is a time chart showing the recording or reproducing operation of the tape recorder which is arranged as described above. A phase detection pulse signal (hereinafter referred to as signal PG(a)) is produced in synchronism with the rotation of the rotary cylinder 2 as shown at a part (a) in FIG. 5. The signal PG(a) is in a rectangular wave form of 30 Hz alternately repeating high (H) and low (L) levels in a cycle of 1/60 sec. Another phase detection pulse signal (hereinafter referred to as signal PG(b)) is opposite in polarity to the signal PG(a) as shown at a part (b). The signal PG(a) is at a high level (H) while the head 3 turns from the point B to the point G as shown in FIG. 3. The signal PG(b) is at a high level (H) while the other head 4 turns from the point B to the point G.
A part (c) in FIG. 5 shows a data reading pulse signal which is obtained from the signal PG(a) and is used for sampling, for every other field, an audio signal of a period corresponding to one field portion (1/60 sec) of a video signal. A part (d) of FIG. 5 shows a signal representing signal processing periods during which the one-field portion of the audio data (or signal) sampled is subjected to signal processing operations such as addition of an error correcting redundant code or the like using a RAM or the like, rearrangement of the data, etc. These periods obtain when this signal is at a high level. A part (e) shows a signal which is at a high level to indicate a data recording period for recording on the tape 1 the recording data obtained through the above-stated signal processing operation.
For example, the temporal flow of the signals indicated in FIG. 5 is as follows: The data is sampled during a period between points of time t1 and t3 (during which the head 3 is moving from the point B to the point G). During a period between points of time between t3 to t5 (during which the head 3 is moving from the point G to the point A), the sampled data is signal processed. Recording is accomplished during a period between points of time t5 and t6 (while the head 3 is moving from the point A to the point B). In other words, the data is recorded by the head 3 in the area CH1 of FIG. 4. Meanwhile, the data which is sampled when the signal PG(b) is at a high level is also signal processed at similar timing and is recorded by the other head 4 in the area CH1.
A part (f) in FIG. 5 shows a phase detection pulse signal (hereinafter referred to as signal PG(f)) representing a phase shifted to a given degree of phase which is 36 degrees in this instance. This signal PG(f) and another signal PG which is not shown but is opposite to the signal PG(f) in polarity are used in recording an audio signal. The audio signal recording is performed as follows: The data sampled during a period between the points of time t2 and t4 is signal processed during another period between the points of time t4 and t6 according to a signal (g) which is shown at a part (g) of FIG. 5 and is then recorded during a period between the points of time t6 and t7 according to a signal (h) which is shown at a part (h) in FIG. 5. In other words, the audio signal is recorded by the head 3 in the area CH2 shown in FIG. 4 while the head 3 is tracing the tape between points B and C. The data which is sampled during a period between the points of time t4 and t7 is likewise recorded by the other head 4 in the area CH2 shown in FIG. 4.
The signal recorded in the area CH2 is reproduced in the following manner:
The head 3 reads out data from the tape 1 according to the signal (h) shown in FIG. 5 during a period between the points of time t6 and t7 (or between t1 and t2). The data which is thus read out is subjected to a signal processing operation which is carried out according to a signal (i) shown in FIG. 5 during a period between the points of time t7 and t8 (or between t2 and t3) in a manner reverse to the signal processing operation performed for recording. In other words, during this period, error correction, etc. are carried out. Following this, during a period between points of time t8 and t9 (or between t3 and t6), a reproduced audio signal is produced in accordance with a signal (j) shown at a part (j) of FIG. 5. It goes without saying that the head 4 meanwhile also performs the reproducing operation at a phase difference of 180 degrees from the above-stated operation to give likewise a reproduced audio signal.
For each of other areas CH3 to CH6, the signal PG(a) is phase shifted by n.times.36 degrees as applicable. Recording or reproduction is then performed on the basis of the phase shifted signal PG(a) irrespective of the travelling direction of the tape.
With the recording and reproducing apparatus of the prior art thus arranged to perform the multi-channel operation, the recordable length of time on a single piece of cassette tape becomes much longer than before. While this is an advantage, it becomes difficult to grasp the recorded states of all the channels. For example, in the case of a single channel, only one erroneous erasure preventing pin is to be broken after completion of recording. Whereas, in the case of a multi-channel arrangement, an erroneous erasure preventing pin must be provided for every channel and must be broken after completion of recording in each of the channels. Therefore, the multi-channel arrangement necessitates use of a complex detecting device and a complex circuit.
In a conceivable method for solving this problem, an erroneous erasure preventing signal is arranged to be recorded on a tape together with information signals. This arrangement, however, necessitate some arrangement for recording and reproduction of the erroneous erasure preventing signal and a circuit for detecting it. Besides, in that event, no erroneous erasure preventing arrangement can be added later on. Further, in the case of an apparatus which is capable of performing recording over such a long period of time as mentioned in the foregoing, it is inconvenient to have many erroneous erasures preventing parts intermittently provided on the tape.